When your boat is plugged into shore power or running a generator, the battery charger(s) will keep your bank charged up. When conditions don’t require that you run the genset, the alternator provides the charge. How do you know if the alternator properly charges the batteries? What can you look for to monitor the alternator’s condition and anticipate problems before a failure occurs?
LOOKING FOR TROUBLE
Let’s begin with the alternator belt(s). An improperly tensioned belt can slip in the pulley, preventing the alternator from reaching the required rpm. For conventional V-belts, a good rule is an eighth of an inch of deflection for every inch of span. For serpentine (grooved) belts, you can use a plastic gauge to test for tension, and to make sure the tensioner on the engine is not jammed or broken.
Look for signs of misalignment or wear—a fine black or gray dust in the immediate area will provide an indication. Since alternators create heat as they work, they have fans behind the pulley to pull air through the alternator. If the belt has been slipping, the alternator can be packed
